GUNNERY. The science and art of handling guns. The science of handling guns consists of exterior and interior ballistics (q.v.) and the discussion of problems arising in connection there with. The art of handling guns includes drill and target practice and the practical problems and other matters connected with them.
To render a gun effective, four points are to be considered: (1) Safety, (2 )accuracy, (3 )destruc tive effect, (4) speed of fire. Safety is necessary, as the knowledge, or even the suspicion, of its un safeness, will demoralize the men who handle it, in addition to which is to be considered the injury it may do if it gives way. The greatest dangers to be apprehended from modern guns are the premature explosion of the charge; a hang-fire (q.v.) and the opening of the breech before ex plosion of the charge; the jamming of a pro jectile in the bore and the blowing off of the muzzle; the use of bad or improper powder, or of proper powder in too great quantities; weak ness in the mount. No other causes should ren der a well-made modern gun dangerous to its crew. Premature explosion of the charge cannot absolutely be prevented, but it is now rendered very unlikely by automatic attachments to the breech mechanism which make it impossible to fire the primer—whether electric or percussion— before the breech is fully closed and locked. The remaining source of danger is the high tempera ture of a gun when heated by rapid firing; the condition of affairs in which a gun becomes so hot that it will set fire to the charge is not im possible, but should be unusual. Turret guns may be cooled by the washing-out hose, which is always handy, and the other guns by the fire hose if necessary. Hang-fires (q.v.) are chiefly dangerous in small pieces, and most of these are automatic or semi-automatic, and will not open until the charge is exploded. The jamming of the projectile may occur in spite of all ordinary precautions; but the damage is usually confined to the part of the gun outside of the ship, and therefore will not injure the members of the crew. The use of bad (i.e. deteriorated) powder is very nearly overcome by the employment of a reliable kind of powder and careful inspection and stow age. As far as weakness of mount is concerned,
there is no excuse for a mount to be so weak as to render firing dangerous to the crew.
Having secured a gun and mount which is safe, we should next desire accuracy. In a field gun the causes of inaccuracy are: (1) Varia tions in the angle of sight; (2) drift (due to ro tation of the projectile) ; (3) wind; (4) jump; (5) axis of trunnions not in the horizontal plane; (6) variations in velocity of projectile due to inequality of the powder; (7) incorrect setting of the sights, due to error in the supposed distance of the object fired at; (8) personal error of the gun pointer, which makes him habitually take too fine or too coarse a sight, etc.; (9) state of the atmosphere (height of barometer and thermome ter and hygrometric conditions) ; (10) effect of strong or defective light upon the sights, etc. In addition to these, guns aboard ship are sub ject to errors due to (11) horizontal movement of the ship and of the enemy; (12) rolling and pitching of the ship. As ships' guns have all the errors of field guns and some very important ones of their own, we need consider them only. The angle of sight is the elevation of the object fired at above the horizontal plane through the gun; the error due to this is usually trifling. This follows from the principle of the 'rigidity of the trajectory,' which may be briefly explained by saying that the range of a gun upon any plane passing through the axis of the trunnions of a gun is practically the same as upon the horizontal plane, if the angle of elevation of the gun above this plane is the same as its elevation above the horizontal; provided always that 'the angle the inclined plane makes with the horizontal is a small one. The drift of a projectile is very con siderable; but it is likewise very regular in amount, and this is definitely known and allowed for by inclining the rear sight-bar to the left through an angle of to 3 degrees, or dropping the left end of the axis of a telescope sight until it is inclined the same amount.